DE102012009219B4 - Battery module, electrical energy system in a motor vehicle and method for operating a battery module - Google Patents

Abstract

Battery module (2, 3), comprising at least two battery cells (BZ1-BZX) connected in series and a DC/DC converter (7), the DC/DC converter (7) having a first input connection (E1) and a second input connection (E2), characterized in that the first input connection (E1) is assigned a first switching element (U1) and the second input connection (E2) is assigned a second switching element (U2), the switching elements (U1, U2) each having an output which is permanently connected to the assigned input connection (E1, E2) of the DC/DC converter (7) and has at least one first and one second input (U11, U12; U21, U22) which can be optionally connected to the output of the changeover switch (U1 , U2) can be switched through, with a respective switching element (S1-SX+1) being arranged on the pole connections of the battery cells (BZ1, BZX), with the positive pole of a first battery cell (BZ1) being connected to the first input ( U11) of the first switching element (U 1) and the second input (U22) of the second switching element (U2) and the negative pole of the battery cell (BZ1) via the switching element (S2) to the second input (U12) of the first switching element (U1) and the first input (U21 ) of the second switching element (U2), the positive pole of an adjacent second battery cell (BZ2) being connected via the switching element , (S2) to the second input (U12) of the first switching element (U1) and the first input (U21) of the second switching element (U2) is connected and the negative pole is connected via the switching element (S3) to the first input (U11) of the first switching element (U1) and the second input (U22) of the second switching element (U2).

Description

The invention relates to a battery module, an electrical energy system in a motor vehicle with such a battery module, and a method for operating a battery module.

Electric or hybrid vehicles include a high-voltage battery for supplying electrical energy to an electronic machine. These high-voltage batteries are usually formed by battery cells being connected in series in order to provide the necessary voltage level. The battery cells are, for example, Li-ion battery cells or double-layer capacitors. On the one hand, these battery cells must be charged and, on the other hand, their voltage levels must not vary too much.

From the WO 2011/070517 A1 an electrical power supply for a consumer is known, which consists of a series connection of battery cells. An inductance with a switch is connected in parallel with each battery cell. Another inductance is arranged opposite the inductances of the battery cells, so that a transformer is formed. An energy store is arranged in parallel with this inductor and is designed, for example, as a capacitor. Furthermore, a charging device, which is not explained in detail, is disclosed, which is connected in parallel to the series connection of the battery cells via a switch and is connected to the inductor via a further switch. This allows different loading modes. On the one hand, the series connection of the battery cells can be electrically connected directly to the charging device. It is also possible to charge the energy of individual battery cells via the transformer. For example, a highly charged individual battery cell can transfer energy to the other side of the transformer and this energy can then be transferred back to another, slightly charged battery cell. Combined charging is also described, where the charging device charges all battery cells simultaneously, but the charging of the individual battery cells is controlled by varying the switching pulses on switches assigned to the battery cells in such a way that all battery cells are at the same voltage level. Such a charging mode is also possible via the other side of the transformer, which is previously charged by the charging device. This energy is then transferred to the battery cell by means of a transformer, with the charging current of the individual battery cell being adjustable by appropriate setting of the switches.

From the DE 10 2009 054 818 A1 a converter for an electrical energy storage system is known, with an energy transmitter, an inverter and an intermediate circuit connected between the energy transmitter and the inverter and having at least one intermediate circuit capacitor, the energy transmitter having a plurality of DC-DC converters which are connected in parallel and/or in series with one another on the intermediate circuit side and each the DC-DC converter can be connected to a respective energy storage module of the energy storage system by means of a first and a second input, the intermediate circuit capacitor being an intermediate store of a storage module equalization circuit formed at least in part by the energy transmitter.

A disadvantage of the known compensating or balancing circuit structures is their large component complexity, which makes them expensive and error-prone.

The invention is based on the technical problem of creating a battery module with a simplified design and an electrical energy system with such a battery module and of making available a method for operating a battery module.

The technical problem is solved by the objects with the features of patent claims 1, 6, 7, 8, 9 and 10. Further advantageous configurations of the invention result from the dependent claims.

The battery module comprises at least two battery cells connected in series and a DC/DC converter, the DC/DC converter having a first input connection and a second input connection, a first switching element being assigned to the first input connection and a second switching element being assigned to the second input connection, wherein the switching elements each have an output which is permanently connected to the assigned input connection of the DC/DC converter and each have at least a first input and a second input which can be selectively switched through to the output of the changeover switch, wherein at the pole connections of the battery cells in each case a switching element is arranged, the positive pole of a first battery cell being connected via the switching element to the first input of the first switching element and the second input of the second switching element, and the negative pole of the battery cell being connected via the switching element to the second input of the first Switching element and the first input of the second switching element is connected, the positive pole of an adjacent second Bat tery cell is connected via the switching element to the second input of the first switching element and the first input of the second switching element and the negative pole is connected via the switching element to the first input of the first switching element and the second input of the second switching element. The switching element for the negative pole of the first battery cell is at the same time the switching element for the positive pole of the second battery cell. Correspondingly, two adjacent battery cells each share a common switching element. Accordingly, a third battery cell is again connected like the first battery cell. Due to the construction according to the invention, the balancing for all battery cells takes place via a single DC/DC converter, with only n+1 switching elements for n battery cells and the two switching elements being required in addition to the DC/DC converter. The direction of the energy transport, ie whether energy is taken from or supplied to the individual battery cell, is simply set by the switching elements. The switching elements are preferably in the form of transistors. The switching elements each represent a multiplexer and can be formed, for example, by means of relays or transistors.

In one embodiment, the switching elements are each switched to the first input or to the second input, i.e. if the first input on the first switching element is switched through, the first input of the second switching element is also switched through. In this case, the switchover elements are preferably activated synchronously.

In a further embodiment, the DC/DC converter is designed as an inverse converter (buck-boost converter). The inverse converter is a boost/buck converter whose output voltage is inverted. The advantage of this DC/DC converter is that its inductance makes it very easy to balance the charge of the battery cells in the battery module without transforming back an output voltage. On the other hand, the energy that was taken from the battery cells for balancing can be made available to other systems very easily, with the voltage being adjusted by the inverse converter.

In a further embodiment, the battery module includes at least one control unit that generates the control signals for the switching elements, the switching elements and the DC/DC converter. For this purpose, the control unit is preferably connected to elements for measuring the battery cell saving. Furthermore, the control unit is preferably connected to at least one other control unit, which transmits an energy requirement of at least one other component, e.g. the on-board electrical system, to the control unit.

In a further embodiment, the battery module has a bridging circuit, by means of which the outputs of the switching elements can be switched directly to the outputs of the DC/DC converter. As a result, the DC/DC converter can be bypassed as required, for example because the on-board electrical system requires a high current which the DC/DC converter cannot carry. In this case, one battery cell or an odd number of battery cells connected in series is connected directly to the output of the DC/DC converter via the switching elements.

The electrical energy system in a motor vehicle comprises at least one battery module, with the output of the DC/DC converter being connected to an on-board electrical system of the motor vehicle and/or to another battery module.

The battery module can serve to support the on-board electrical system and, for example, serve as a redundant power supply. Various methods are possible, which can also be combined with one another.

In a first embodiment, energy drawn from the battery cells for balancing is supplied to the on-board electrical system as a redundant energy supply. This can be done permanently or only as needed. Furthermore, it can also be provided that this energy supply only serves to supply the on-board electrical system consumers with quiescent current.

In a further embodiment, if the power supply to the on-board electrical system drops or fails, the on-board electrical system is supplied from the battery cells via the DC/DC converter. In this case, more energy is drawn from the battery cells than would be necessary for pure balancing.

In a further embodiment, to balance the battery cells, a battery cell to be discharged is connected to the DC/DC converter, with the energy drawn being stored in at least one inductance of the DC/DC converter, the battery cell then being separated from the DC/DC converter and a battery cell to be charged is connected to the DC/DC converter.

In a further embodiment, the battery module comprises at least three battery cells, with an odd number of battery cells connected in series being connected to the switching elements at the same time. This procedure can Both for balancing and for supplying other components, such as the on-board electrical system, are used, with the series circuit being able to be connected directly to the output of the DC/DC converter via the switching elements if necessary if the bypass circuit is present. This allows faster balancing or faster energy transport to the on-board electrical system, since the voltage does not have to be stepped up as much or at all.

The invention is explained in more detail below using a preferred exemplary embodiment. The only figure shows a schematic block diagram of an electrical energy system in a motor vehicle.

The electrical energy system 1 of a motor vehicle includes a first battery module 2, at least one additional battery module 3 and an electrical system 4. The electrical system 4 includes a power supply, which is designed as a double-layer capacitor 5 in the illustrated embodiment. However, the power supply can also consist of one or more battery cells or a battery. The voltage supply of the electrical system 4 is used to supply energy to consumers 6 of the vehicle electrical system, with only one electrical system consumer 6 being shown as an example. The electrical system consumers 6 are, for example, control devices and lighting devices.

The two battery modules 2, 3 have the same structure and are connected in series with one another and form a traction battery for the motor vehicle. The exact structure will now be explained in more detail on the basis of the first battery module 2 .

The battery module 2 includes X battery cells BZ1-BZX, which are connected in series with one another. In this case, each pole of the battery cells BZ1-BZX is assigned a switching element S1-SX+1. In this case, for example, the switching element S1 is assigned to the positive pole of the battery cell BZ1. The switching element S2 is assigned to the negative pole of the battery cell BZ1 and to the positive pole of the adjacent battery cell BZ2. Finally, the switching element SX+1 is assigned to the negative pole of the battery cell BZX. Furthermore, the battery module 2 includes a DC/DC converter 7. The DC/DC converter 7' includes a first input connection E1 and a second input connection E2. Furthermore, the DC/DC converter 7 includes a first output connection A1 and a second output connection A2. The DC/DC converter 7 also includes a switching element S, an inductor L, a diode D and a capacitor C. The switch S, the inductor L, the diode D and the capacitor C are in the form of an inverse converter (buck-boost converter ) connected, the switch S being controlled by a corresponding PWM signal in order to set the output voltage high or low.

The battery module 2 further comprises a first switching element U1 and a second switching element U2. The output of the first switching element U1 is permanently connected to the first input connection E1 of the DC/DC converter 7 . The first switching element U1 includes two inputs U11, U12 and the second switching element U2 includes two inputs U21, U22. In this case, either the respective first input U11, U21 is switched through to the input connections E1, E2 or the respective second input U21, U22.

Finally, the battery module 2 also includes a control unit 8, which controls the switching elements S1-SX+1 of the battery cells BZ1-BZX, the switching elements U1, U2 and the switch S of the DC/DC converter 7. It should be noted that in principle it is also possible to design control unit 8 as a higher-level control unit for a plurality of battery modules 2, 3, although assignment to one battery module has the advantage of greater reliability. It should also be noted that switching elements or switchover elements can also be arranged at the outputs A1, A2 of the battery module 2, 3 in order to be able to disconnect a battery module 2, 3 or optionally connect it to various components.

During operation, the control device 8 detects the voltages across the individual battery cells BZ1-BZX. If the control unit 8 now determines that, for example, the battery cell BZ1 has too much compared to the other battery cells BZ2-BZX. has a high voltage, energy must be drawn from it. For this purpose, the switching elements S1 and S2 are closed. Furthermore, the switching elements U1, U2 are connected to the first inputs U11, U21. Appropriate PWM control of the switch S then causes a current to flow out of the first battery cell. BZ1 in the DC/DC converter 7. This energy can now be used in different ways. For example, the output voltage of the DC/DC converter 7 of the battery module 2 can be set to the charging voltage of the double-layer capacitor 5 and this can be charged. As a result of this measure, the on-board electrical system 4 is supported or redundantly supplied with voltage. This redundant voltage supply makes it possible to place lower demands on the primary energy supply of the on-board electrical system 4, for example in terms of storage capacity. It is possible that Limiting the supply of energy from the battery module 2, 3 to the on-board electrical system 4 depending on the situation. For example, provision can be made to cover only the retirement requirement of the on-board electrical system 4 . On the other hand, provision can also be made for the battery module 2, 3 to support the vehicle electrical system 4 whenever it is necessary, ie also while driving, by making balancing energy available to the vehicle electrical system. Finally, it can also be provided that energy is not only made available to the vehicle electrical system 4 for balancing the battery cells BZ1-BZX, but also that energy is also taken from the battery cells BZ1-BZX for support as required. Due to the controllability of each individual battery cell BZ1-BZX of the battery module 2, 3, the vehicle electrical system 4 can be supplied with electricity even if individual battery cells BZ1-BZX fail, so that the battery module 2, 3 represents an extremely fail-safe energy supply for the vehicle electrical system 4.

If, on the other hand, energy is now to be transmitted within the battery module 2, 3, the battery cell BZ1-BZX, from which the energy is drawn, is first connected to the DC/DC converter 7 with the correct sign.

Assuming now that energy is to be transferred from the second battery cell BZ2 to the first battery cell BZ1, the switching elements S2 and S3 are closed. The switching elements U1, U2 are connected to the second inputs U12, U22. When the switching element S of the DC/DC converter 7 is closed, a current that builds up a negative voltage at the inductance L then flows. The switching element S3 is then opened and S1 is closed. By closing S, a current flows into the first battery cell BZ1, which reduces the voltage across the inductance L, with the correct sign.

The battery module 2, 3 thus allows a serial activation of the battery cells BZ1-BZX for balancing the battery cells BZ1-BZX with each other as well as a power supply of components connected to the outputs A1, A2 of the DC/DC converter 7, such as for example the vehicle electrical system 4.

Furthermore, it is also possible not only to connect one battery cell BZ1-BZX to the inputs of the switchover elements, but to simultaneously apply a series connection of an odd number of battery cells BZ1-BZX to the switchover elements U1, U2. For example, if energy is to be taken from the battery cells BZ1-BZ3, then S1 and S4 (not shown) can be closed. As a result, the series connection of BZ1, BZ2 and BZ3 is due to the switching elements U1, U2. Their energy can then be stored in the inductance L and fed back into one or more battery cells BZ1-BZX (likewise a series connection of an odd number of battery cells). Alternatively, this energy can also be made available to other components, such as the on-board electrical system, as described above. Since the input voltage of the DC/DC converter 7 is now higher, the voltage must now be lower or not increased at all.

Claims (10)

Battery module (2, 3), comprising at least two battery cells (BZ1-BZX) connected in series and a DC/DC converter (7), the DC/DC converter (7) having a first input connection (E1) and a second input connection (E2), characterized in that the first input connection (E1) is assigned a first switching element (U1) and the second input connection (E2) is assigned a second switching element (U2), the switching elements (U1, U2) each having an output, which is permanently connected to the associated input connection (E1, E2) of the DC/DC converter (7) and has at least one first and one second input (U11, U12; U21, U22) which can be optionally connected to the output of the changeover switch ( U1, U2) can be switched through, with a switching element (S1-SX+1) being arranged on each of the pole connections of the battery cells (BZ1, BZX), with the positive pole of a first battery cell (BZ1) being connected to the first input via the switching element (S1). (U11) of the first switching element (U1) and the second input (U22) of the second switching element (U2) and the negative pole of the battery cell (BZ1) via the switching element (S2) to the second input (U12) of the first switching element (U1) and the first input ( U21) of the second switching element (U2), the positive pole of an adjacent second battery cell (BZ2) being connected via the switching element , (S2) to the second input (U12) of the first switching element (U1) and the first input (U21) of the second Switching element (U2) is connected and the negative pole via the switching element (S3) to the first input (U11) of the first switching element (U1) and the second input (U22) of the second switching element (U2) is connected. battery module after claim 1 , characterized in that the switching elements (U1, U2) are connected to the first input (U11, U21) or the second input (U12, U22). battery.module.after claim 1 or 2 , characterized in that the DC / DC converter (7) is designed as an inverse converter. Battery module according to one of the preceding claims, characterized in that the battery module comprises at least one control unit (8) which transmits the control signals for the switching elements (S1-SX+1), the switching elements (U1, U2) and the DC/DC converter ( 7) generated. Battery module according to one of the preceding claims, characterized in that the battery module (2, 3) has a bypass circuit, by means of which the outputs of the switching elements (U1, U2) are connected directly to the outputs (A1, A2) of the DC/DC converter (7 ) are switchable. Electrical energy system in a motor vehicle, characterized in that the electrical energy system (1) has at least one battery module (2) according to one of Claims 1 until 4 comprises, wherein the output (A1, A2) of the DC / DC converter (7) with an electrical system (4) of the motor vehicle and / or another battery module (3) is connected. Method for operating a battery module claim 1 , characterized in that energy taken from the battery cells (BZ1-BZX) for balancing is made available to an on-board electrical system (4). Method for operating a battery module claim 1 , characterized in that in the event of a drop in or failure of the energy supply to an on-board electrical system (4), the on-board electrical system (4) is supplied from the battery cells (BZ1-BZX) via the DC/DC converter (7). Method for operating a battery module claim 1 , characterized in that in order to balance the battery cells (BZ1-BZX), a battery cell (BZ1-BZX) to be discharged is connected to the DC/DC converter (7), the energy drawn being used in at least one inductance (L) of the DC/ DC converter (7) is stored, then the battery cell (BZ1-BZX) is separated from the DC/DC converter (7) and a battery cell to be charged (BZ1-BZX) is connected to the DC/DC converter (7). Method for operating a battery module claim 1 , wherein the battery module (2, 3) comprises at least three battery cells (BZ1-BZX), characterized in that an odd number of series-connected battery cells is connected simultaneously to the switching elements (U1, U2).

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